LEA-M8S / LEA-M8T - Hardware integration manual
UBX-15030060 - R06 Design Page 17 of 33
Production information
The current active antenna status can be determined by polling the UBX-MON-HW monitor
command. If an antenna is connected, the initial state after power-up is “Active Antenna OK.”
The module firmware supports an active antenna supervisor circuit, which is connected to the
ANT_DET_N pin. For an example of an open circuit detection circuit, see Figure 13.
"high" = Antenna detected (antenna consumes current)
"low" = Antenna not detected (no current drawn)
Status reporting
At startup, and on every change of the antenna supervisor configuration, the LEA-M8S module will
output an NMEA ($GPTXT) or UBX (INF-NOTICE) message with the internal status of the antenna
supervisor (disabled, short detection only, enabled).
Active antenna control enabled
Short circuit detection Enabled
Open circuit detection enabled
Short circuit power down logic enabled
Automatic recovery from short state
Table 4: Active antenna supervisor message on startup (UBX binary protocol)
☞ To activate the antenna supervisor, use the UBX-CFG-ANT message. For further information,
refer to the u-blox 8 / u-blox M8 Receiver Description Including Protocol Specification [3].
Similar to the antenna supervisor configuration, the status of the antenna supervisor will be reported
in an NMEA ($GPTXT) or UBX (INF-NOTICE) message at start-up and on every change.
2.4.3 Power and short detection antenna supervisor
If a suitably dimensioned R_BIAS series resistor is placed in front of the V_ANT pin, a short circuit can
be detected in the antenna supply. The detection happens inside the u-blox M8 module, after which
the antenna supply voltage will be immediately shut down. Afterwards, periodic attempts to re-
establish antenna power are made by default.
An internal switch (under control of the receiver) can turn off the supply to the external antenna
whenever it is not needed. This feature helps to reduce power consumption in power save mode.
☞ To configure the antenna supervisor, use the UBX-CFG-ANT message. For further information,
see the u-blox 8 / u-blox M8 Receiver Description Including Protocol Specification [3].
⚠ Short circuits on the antenna input without limitation (R_BIAS) of the current can result in
permanent damage to the receiver! Therefore, it is mandatory to implement an R_BIAS in all risk
applications, such as in situations where the antenna can be disconnected by the end-user or the
antenna cables are long.
☞ In case VCC_RF voltage does not match with the antenna supply voltage, use a filtered external
supply as shown in Figure 12.
Supply from VCC_RF
Figure 11 shows an active antenna supplied from the LEA-M8S / LEA-M8T module.
LEA-M8S module includes a built in antenna bias supply for nominal 3 V antennas enabled by linking
the filtered VCC_RF supply output pin to the V_ANT antenna supply input pin with a 10 Ohm resistor
in series. The module then controls the power supply to the antenna, applying power whenever the
receiver is active and removing power during power-save idle times and if a short-circuit is detected.
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